[tfjs-core] Support newAxisMask in stridedSlice and make squeeze consistent with TF Py

[dsmilkov]

• Add support for the newAxisMask param in stridedSlice(). Because stridedSlice() is difficult to implement correctly, and all backends have to repeat fragile logic, shift common preprocess and postprocess logic to the logical stridedSlice op and simplify the actual kernel.
• Make tf.squeeze(x, axis) consistent with TF when axis is empty array.

These fixes were found by running a converted TF model in the browser.

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This change is 

[nsthorat]

Reviewed 9 of 9 files at r1.
Reviewable status: complete! 1 of 1 approvals obtained (waiting on @dsmilkov, @nsthorat, and @pyu10055)

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tfjs-core/src/ops/strided_slice_test.ts, line 65 at r1 (raw file):

    const ellipsisMask = 0;
    const newAxisMask = 10;     // 1010
    const shrinkAxisMask = 20;  // 10100

you can use his here and elsewhere

0b10100

[dsmilkov]

Reviewable status: complete! 1 of 1 approvals obtained (waiting on @pyu10055)

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tfjs-core/src/ops/strided_slice_test.ts, line 65 at r1 (raw file):

Previously, nsthorat (Nikhil Thorat) wrote…

you can use his here and elsewhere

0b10100

Done